CONTACT STRESS ANALYSIS OF THE NATIVE RADIAL HEAD AND RADIAL HEAD IMPLANTS by Sunghwan Kim B. S. in Mechanical Engineering, Sogang University, Korea, 1999 M. S. in Mechanical Engineering, University of Southern California, 2006 Submitted to the Graduate Faculty of Swanson School of Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 2014 UNIVERSITY OF PITTSBURGH SWANSON SCHOOL OF ENGINEERING This dissertation was presented by Sunghwan Kim It was defended on April 29, 2014 and approved by Richard Debski, Ph.D., Associate Professor, Department of Bioengineering Rakié Cham, Ph.D., Associate Professor, Department of Bioengineering Patrick Smolinski, Ph.D., Associate Professor, Department of Mechanical Engineering Dissertation Director: Mark Miller, Ph.D., Associate Research Professor, Department of Mechanical Engineernig ii Copyright © by Sunghwan Kim 2014 iii CONTACT STRESS ANALSIS OF THE NATIVE RADIAL HEAD AND RADIAL HEAD IMPLANTS Sunghwan Kim, PhD University of Pittsburgh, 2014 A radial head fracture is a common fracture of the elbow joint most frequently caused by a fall on an outstretched arm. When the radial head is comminuted and reconstruction is not viable, radial head replacement is often the preferred option. There are basically two choices for the radial head implants: monoblock and bipolar. However, little research examining the performance of available radial head implants has been conducted. In this study, a finite element model for the intact elbow joint extracted from CT scans of a cadaveric elbow was created. The constructed FE model was validated with cadaveric experiments using Fuji pressure sensitive film. Then, two different implant models were generated by replacing the radial head with monoblock and bipolar implants. Contact stress and area for each model were calculated and compared under various loading conditions in the contact areas between the radial head and the capitellum of the humerus, and between the radial head and the radial notch of the ulna. A significant difference was found in both maximum contact stress and contact area between the native elbow and two types of implants. Contact stress for monoblock was higher than that for bipolar and vice versa for contact area. FE predictions showed the same pattern as measurements from Fuji analysis did although they overestimated the maximum contact stress and underestimated the contact area compared to the Fuji film experimental results. iv TABLE OF CONTENTS PREFACE .................................................................................................................................. XII 1.0 INTRODUCTION ........................................................................................................ 1 2.0 BACKGROUND .......................................................................................................... 3 2.1 ANATOMY AND BIOMECHANICS OF THE ELBOW ............................... 3 2.1.1 Radial head ....................................................................................................... 7 2.1.2 Capitellum ........................................................................................................ 8 2.2 BONE .................................................................................................................... 9 2.3 ARTICULAR CARTILAGE ............................................................................ 10 2.4 LIGAMENT ....................................................................................................... 12 2.5 RADIAL HEAD FRACTURES ........................................................................ 12 2.6 TREATMENTS FOR RADIAL HEAD FRACTURE ................................... 13 2.6.1 Radial head excision ...................................................................................... 14 2.6.2 Open reduction and internal fixation [ORIF] ............................................. 14 2.6.3 Radial head arthroplasty .............................................................................. 15 2.7 RADIAL HEAD IMPLANTS ........................................................................... 16 2.8 FINITE ELEMENT ANALYSIS ..................................................................... 19 2.8.1 Contact analysis ............................................................................................. 20 2.8.2 FE contact parameters .................................................................................. 22 2.8.2.1 FKN and FKT ...................................................................................... 22 2.8.2.2 FTOLN and SLTO .............................................................................. 23 2.8.2.3 PMAX and PMIN ................................................................................ 23 v 2.9 FUJI PRESSURE SENSITIVE FILM ............................................................. 23 3.0 BACKGROUND REVIEW OF CONTACT ANALYSIS ...................................... 25 3.1 JOINT PRESSURE AND CONTACT AREA ................................................ 25 3.2 MONOBLOCK VS BIPOLAR ......................................................................... 29 3.3 CLINICAL OUTCOMES OF RADIAL HEAD REPLACEMENT ............. 31 3.4 FE MODELING OF HUMAN JOINTS .......................................................... 32 3.5 CARTILAGE THICKNESS ............................................................................. 34 4.0 NATIVE RADIAL HEAD FE ANALYSIS ............................................................. 35 4.1 CREATION OF THE 3-D ELBOW MODEL ................................................ 35 4.2 FE MODEL DESCRIPTION ........................................................................... 37 4.3 CONVERGENCE .............................................................................................. 39 4.4 SENSITIVITY STUDY ..................................................................................... 47 4.4.1 Cartilage thickness ........................................................................................ 47 4.4.2 Cartilage material properties ....................................................................... 55 4.4.3 Bone material properties............................................................................... 62 4.4.4 Ligament stiffness .......................................................................................... 66 5.0 RADIAL HEAD IMPLANT FE ANALYSIS .......................................................... 70 5.1 MONOBLOCK IMPLANT MODEL .............................................................. 71 5.2 BIPOLAR IMPLANT MODEL ....................................................................... 75 6.0 VALIDATION OF THE FE MODEL ..................................................................... 79 6.1 EXPERIMENTAL SETTING .......................................................................... 79 6.2 FUJI FILM ANALYSIS .................................................................................... 82 6.3 COMPARISON BETWEEN FE AND FUJI FILM ....................................... 85 vi 7.0 DISCUSSION ............................................................................................................. 89 8.0 CONCLUSION AND FUTURE WORK ................................................................. 95 APPENDIX A .............................................................................................................................. 97 APPENDIX B ............................................................................................................................ 100 BIBLIOGRAPHY ..................................................................................................................... 110 vii LIST OF TABLES Table 1. Fuji film pressure ranges ................................................................................................. 24 Table 2. Material properties of the bone and soft tissues ............................................................. 39 Table 3. Number of elements for 6 different meshes .................................................................... 41 Table 4. Maximum contact stress and contact area calculated from Fuji film ............................. 84 viii LIST OF FIGURES Figure 1. Anatomy of the elbow joint ............................................................................................. 4 Figure 2. Elbow flexion and extension ........................................................................................... 5 Figure 3. Supination and pronation of the forearm ......................................................................... 5 Figure 4. MCL complex of the elbow joint .................................................................................... 6 Figure 5. LCL complex of the elbow joint ..................................................................................... 7 Figure 6. Anatomy of the radial head ............................................................................................. 8 Figure 7. Anisotropic behavior of cortical bone in tension in four directions .............................. 10 Figure 8. Structure of articular cartilage ....................................................................................... 11 Figure 9. Broberg-Morrey modified radial head fracture classification ....................................... 13 Figure 10. Incision for radial head replacement ..........................................................................